1. Field of the Invention
The present invention relates to a lift-off positive resist composition.
This application claims priority from Japanese Patent Application No. 2004-102046 filed on Mar. 31, 2004, the disclosure of which is incorporated by reference herein.
2. Description of the Related Art
In the production of semiconductor devices and light crystal display devices, a fine working technique based on a lithography technique is used. A three-dimensional fine working technique employing the lithography technique is referred to as micromachining and is used in the production of high-grade portable systems in which various elements such as sensors, circuits and fine structures are integrated on a substrate, for example, so-called MEMS and MRAM.
As one of applications of such a lithography technique, a lift-off method is exemplified. For example, the lift-off method is used in the production of fine structures in the lead portion (head portion for read-out) of a magnetic head of a magnetic recording medium (see, for example, Patent Document 1).
In FIG. 1A to FIG. 1E, schematic views (side sectional views) showing the respective steps of forming a magnetic head are shown.
First, as shown in FIG. 1A, a magnetic film 2′ is laminated on a substrate 1, and then a base film 3′, which is soluble in an alkali developer solution, and a resist film 4′ are sequentially laminated thereon.
The resist film 4′ is subjected to selective exposure via a mask pattern using a KrF excimer laser. When alkali development is conducted, a predetermined range (the exposed area in the case of a positive one, or the non-exposed area in the case of a negative one) of the resist film 4′ is dissolved and removed to obtain a resist pattern 4. At this time, the base film 3′ located under the removed portion of the resist film 4′ is also removed with an alkali developer solution to form a base pattern 3; however, the base film 3′ usually has alkali solubility higher than that of the resist film 4′, and the width W1 of the base pattern 3 is smaller than the width W2 of the resist pattern 4. Due to a difference in dissolution rate, as shown in FIG. 1B, a lift-off pattern 5 having a battledore-shaped profile comprising a base pattern 3 having a small width and a resist pattern 4 having a larger width can be obtained.
When ionic etching is conducted using the lift-off pattern 5 as a mask, as shown in FIG. 1C, the magnetic film 2′ around the lift-off pattern 5 is etched to form a magnetic film pattern 2 under and around the lift-off pattern 5. Ion milling is often used as ionic etching.
When sputtering is further conducted, as shown in FIG. 1D, an electrode film 6 is formed on the lift-off pattern 5 and the substrate 1 around the magnetic film pattern 2.
Finally, the base pattern 3 is dissolved by using an alkali developer solution to remove the resist pattern 4, and thus the lift-off pattern 5 is removed (lifted-off). Due to lifing-of the lift-off pattern 5, as shown in FIG. 1E, a magnetic head 10 comprising a substrate 1, a magnetic film pattern 2 having a predetermined width formed on the substrate, and an electrode film 6 formed around the substrate is obtained.
Patent Document 1: Japanese Patent Application, First Publication No. 2002-110536
Currently, demands for fine working have increased more and more. For example, it is required to attain fine working of a magnetic head so as to improve recording density of a magnetic recording medium. Also, it is required to form a fine resist pattern (Iso pattern) thereby to form a fine magnetic film pattern so as to attain fine working of the magnetic head.
However, a conventionally used positive resist composition has a problem that a fine lift-off pattern cannot be formed because sufficient fine working cannot be performed.
As one of techniques of performing fine working, fine working of a resist film is proposed. However, a conventionally used positive resist composition has a problem that, because of insufficient resistance to ionic etching such as ion milling, thickness loss of the resist film occurs and rectangularity of the resist pattern becomes worse, and thus the substrate and the magnetic film cannot be sufficiently etched.
There also arises a problem that fine control of the size of the width W1 (see FIG. 1B) of the base pattern 3 in the case of formation of a lift-off pattern is conducted with difficulty and the base pattern 3 becomes too thin due to over-etching causing pattern falling.